Importing a disk image into XCP-ng/XenServer is rather easy, you just need to find the correct VDI and import it using the appropriate `xe vdi-import`. In my case I wanted to test the current OpenWRT release, so:
# xe vdi-list uuid ( RO) : <vdi-uuid> name-label ( RW): OpenWRT name-description ( RW): sr-uuid ( RO): <sr-uuid> virtual-size ( RO): <size> sharable ( RO): false read-only ( RO): false # xe vdi-import uuid=<vdi-uuid> filename=openwrt-combined-ext4.img
That’s it: OpenWRT is installed on Xen and already bootable. At this point you can even mount the OpenWRT drive and resize its partition to fully use the remainder of the space you allocated.